COMBINED 3-IN-1 SCIATIC NERVE BLOCK - BLO CKING EFFICACY, SERUM CONCENTRATIONS AND SIDE-EFFECTS AFTER 700 MG MEPIVACAINE 1-PERCENT WITHOUT OR WITH EPINEPHRINE OR 700 MG PRILOCAINE 1-PERCENT/

A high dose of local anaesthetic is necessary for the combined ''3-in- 1''/sciatic nerve block. Prilocaine is recommended for its low toxicit y. However, in some patients prilocaine results in pronounced methaemo globin formation due to toludine. Little has been known hitherto about the use of high-dose mepivacaine for the combined 3-1/sciatic nerve b lock. This study was undertaken to compare the use 700 mg mepivacaine 1% and 700 mg prilocaine 1%. Methods. The study was approved by the et hics committee of our hospital. Once their informed consent had been o btained in writing 3 X 20 patients (ASA 1-2) undergoing planned surger y on the foot or ankle joint were enrolled in the study. The patients were randomized to the following three groups on a double-blind basis: group 1.700 mg mepivacaine without epinephrine; group 2.700 mg mepiva caine with 0.2 mg epinephrine (1:350000); group 3.700 mg prilocaine 1% . Arterial blood samples for determination of local anaesthetic serum levels were collected over a 120-min period. We determined methaemoglo bin and oxygen saturation before and 120 min after the blockade and co ntinued these measurements for 6 h in group 3. At 15-min intervals, al l patients were questioned about early signs of toxicity. The perioper ative monitoring including blood pressure, ECG and pulse oximetry. Dat a were analysed using ANOVA and Student's t-test, P<0.05 considered st atistically significant. Results. The blocking efficacy did not differ among the groups (groups 1, 2, 3: 90%, 95%, 90%), The maximum mepivac aine serum level in group 1 was 3.91 mu g/ml +/- 0.95 and 2.94 mu g/,m l +/- 0.58 in group 2 (Fig. 2). Over the entire observation period the addition of epinephrine resulted in a significant reduction of the se rum level (between 60.3% at t=15 min and 19.7% at t=120 min). In the p rilocaine group the maximum serum level was 2.07 mu g/ml +/- 0.56, sig nificantly less than in either mepivacaine group. No patient showed si gns or symptoms of local anaesthetic toxicity. In the prilocaine group there was wide variation in methaemoglobin formation among the patien t, with a median of 10.1% (Fig, 3, Table 3). Three patients showed a m aximum methaemoglobinemia between 16% and 17%. Five patients were stil l cyanotic after 6 h when they were transferred to the ward. The fract ional SaO(2) values amounted to 88% (median) with a minimum of 80.3%. Conclusion. Both mepivacaine 1% and prilocaine 1% are appropriate loca l anaesthetics for the combined 3-in-1/sciatic nerve block at a dose o f 700 mg. There was no difference in the blocking efficacy. No patient showed clinical signs or symptoms of a local anaesthetic toxicity. Fo llowing prilocaine we are sometimes faced with high methaemoglobinemia , which may necessitate prolonged monitoring.